1. Field of the Invention
The present invention relates to a monitoring circuit for a light emission device such as a laser diode.
2. Related Background Art
It has been known to use an optical-power meter to monitor an optical-output in order to maintain and inspect a laser diode. The optical-powermeter usually comprises a photo-sensing device such as a photo-diode. An optical-output of the laser diode is converted to an optical-current by the photo-diode, and the optical-output is monitored based on the optical-current.
However, the optical-powermeter is not provided in an actually operated optical communication system and it should be connected wherever the measurement is required, and furthermore the operation of the system, it is not possible to monitor the optical-output of the laser diode. Accordingly, a technique for monitoring in a simple way has been designed. Particularly in a transmission service of a multi-channel video signal and a CATV system which offers a bilateral data communication service, many optical transmitters are used and hence many laser diodes are necessarily used. Accordingly, a technique which permits the monitoring during the operation of the system is required.